| K a Estates (Essex) Limited | Real estate | 2011 |
| K J F a Limited | Administrative & support | 2025 |
| K Joyner Ltd | Professional & scientific | 2018 |
| K&K Facades Ltd | Construction | 2011 |
| K.P.C Electrical Limited | Construction | 2012 |
| Kai's Trading Limited | Wholesale & retail | 2014 |
| Kaizen ERP Consulting Limited | Information & communication | 2026 |
| Kamal Real Estates Ltd | Real estate | 2023 |
| KAN Zhong GUO (UK) Limited | Information & communication | 2009 |
| Kana Group Ltd | Real estate | 2026 |
| Kandhal & Aabhal Ltd | Other services | 2026 |
| Kaps Finishing Limited | Manufacturing | 2011 |
| Karemza Homes Ltd | Real estate | 2019 |
| Karemza Ltd | Health & social care | 2016 |
| Karen Bruce Productions Limited | Arts & recreation | 2000 |
| Karve Capital Ltd | Financial services | 2020 |
| KAS Healthcare Ltd | Health & social care | 2024 |
| KAT Autos Limited | Wholesale & retail | 2020 |
| Kathleen Christa Robson Ltd | Health & social care | 2018 |
| Katie James Management Limited | Real estate | 2023 |
| Kaufman Consultancy Ltd | Wholesale & retail | 2022 |
| KB GAS and Heating Ltd | Construction | 2023 |
| KC Construction & Maintenance Limited | Construction | 2019 |
| KC Print Services Ltd | Manufacturing | 2026 |
| Kcbe Consulting Limited | Professional & scientific | 2025 |
| Kdmac Properties Ltd | Real estate | 2025 |
| Keating Solutions Ltd | Professional & scientific | 2026 |
| KEB Limited | Professional & scientific | 2006 |
| Keep IT Local Marketing Ltd | Information & communication | 2021 |
| Keith Archers Tree Care Specialists Limited | Agriculture & fishing | 1999 |
| Keith Sparling & Associates Ltd | Health & social care | 2010 |
| Kelly Contracts Ltd | Construction | 2008 |
| Kelly Well Ltd | Hospitality | 2024 |
| Kelly Winder Limited | Professional & scientific | 2017 |
| Kemi Anna Productions Ltd | Information & communication | 2022 |
| Kemy Solutions Ltd | Wholesale & retail | 2021 |
| Kendall & Hughes Limited | Administrative & support | 2019 |
| Kensa Consulting Ltd | Professional & scientific | 2016 |
| Kent Car Confidence Ltd | Wholesale & retail | 2024 |
| Kent Rhodes Action Ltd | Professional & scientific | 2009 |
| Kernal Creative Limited | Professional & scientific | 2009 |
| Kestal Projects Limited | Construction | 2005 |
| Keto Chefs Limited | Manufacturing | 2020 |
| Kettle and Crown Limited | Wholesale & retail | 2026 |
| Key Events Essex Limited | Arts & recreation | 2021 |
| Key Sports Education Limited | Administrative & support | 2015 |
| KFH Electrical Services Ltd | Construction | 2008 |
| KGB Facility Services Ltd | Administrative & support | 2012 |
| Khakhar Associates Ltd | Professional & scientific | 2015 |
| Kidstown Organics Ltd | Wholesale & retail | 2019 |
| Kimba Consultancy Limited | Construction | 2019 |
| Kimura Consultants Ltd | Professional & scientific | 2025 |
| Kinetic TKD Limited | Information & communication | 2009 |
| King & Carter Property Ltd | Real estate | 2025 |
| King Installations (Essex) Limited | Construction | 2021 |
| Kings Permanent Recruitment Ltd | Administrative & support | 2006 |
| Kingshott School Trust Limited | Education | 1980 |
| Kingsmoore Projects Ltd | Construction | 2025 |
| Kingsway Autos Limited | Other services | 1964 |
| Kinkade Ltd | Wholesale & retail | 2025 |
| Kirillov Property Management Limited | Real estate | 2019 |
| Kiromubo Limited | Information & communication | 2024 |
| Kitchen and Bathroom Installations Ltd | Construction | 2025 |
| Kitestorm Investments Limited | Real estate | 2020 |
| Kitted OUT Teamwear Limited | Wholesale & retail | 2018 |
| Kitti Robinson Designs Limited | Manufacturing | 2011 |
| KJR Complete Services Ltd | Construction | 2012 |
| Kkams Beauty Ltd | Other services | 2011 |
| Klas Financial Limited | Financial services | 2025 |
| Klevett Ltd | Financial services | 2025 |
| Klogan Investments Ltd | Real estate | 2023 |
| KMI Financial Services Limited | Professional & scientific | 2010 |
| KMS Distributions Limited | Wholesale & retail | 2006 |
| KMS Roxwell Limited | Construction | 2014 |
| KN Plumber Ltd | Construction | 2026 |
| KN Real Estate Ltd | Real estate | 2026 |
| Knight Build Limited | Construction | 1994 |
| Knight Developers Limited | Construction | 2016 |
| Knight Homes & Developments Limited | Construction | 1997 |
| Knight Maintenance Specialists Ltd | Administrative & support | 2024 |
| Knight Plant Limited | Construction | 2004 |
| Knight Property Investors Ltd | Real estate | 2023 |
| Knight Scaffold Services Limited | Construction | 2004 |
| Knight Young Services Limited | Construction | 2019 |
| Knightmaster Enterprises UK Limited | Information & communication | 1994 |
| Knightorque Limited | Wholesale & retail | 2019 |
| Knightowl Limited | Administrative & support | 2021 |
| Knock About Padel Ltd | Other services | 2025 |
| Knock OUT Crewing Limited | Arts & recreation | 2025 |
| KO Child Protection Services Limited | Public administration | 2015 |
| KPA Design Limited | Administrative & support | 2020 |
| KR Henning Project Management Services Limited | Professional & scientific | 2007 |
| Krazuk Property Holdings Ltd | Real estate | 2023 |
| KRB Data Limited | Information & communication | 2010 |
| Krisp & Klean Services Limited | Administrative & support | 2017 |
| Krystle Flower Design Limited | Wholesale & retail | 2013 |
| Ksenia Style Limited | Wholesale & retail | 2002 |
| KSL Properties Ltd | Real estate | 2018 |
| Kube Global Solutions Limited | Wholesale & retail | 2015 |
| Kube Packaging Limited | Administrative & support | 2016 |